Cyclodextrin-polyoxometalate ionic liquid inclusion complex flame retardant additive for making a low smoke zero halogen compound

ABSTRACT

Embodiments of a flame retardant compound are provided. The flame retardant compound includes a polymer base resin and a flame retardant additive distributed within the polymer base resin. The flame retardant additive includes inclusion complexes that are made of at least one guest molecule and at least one carbonific host molecule. The at least one guest molecules is a polyoxometalate ionic liquid. The flame retardant compound achieves a limiting oxygen index of at least 25% according to ISO 4589. Additionally, embodiments of a flame retardant cable are provided that utilize the flame retardant compound as a jacketing material.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/US2018/044339 filed Jul. 30, 2018, which claims the benefit ofpriority of U.S. Provisional Application Ser. No. 62/539,765, filed Aug.1, 2017, the content of which is relied upon and incorporated herein byreference in its entirety.

BACKGROUND

The disclosure relates generally to flame retardant compounds and moreparticularly to a thermoplastic flame retardant compound. Flameretardant materials are used to protect combustible materials, such asplastics or wood, from fire damage and heat. Additionally, flameretardant materials have been used to protect materials that lose theirstrength when exposed to high temperatures, such as steel.

SUMMARY

In one aspect, embodiments of a flame retardant compound are provided.The flame retardant compound includes a polymer base resin and a flameretardant additive distributed within the polymer base resin. The flameretardant additive includes inclusion complexes that are made of atleast one guest molecule and at least one carbonific host molecule. Theat least one guest molecules is a polyoxometalate ionic liquid. Theflame retardant compound achieves a limiting oxygen index of at least25% according to ISO 4589.

In another aspect, embodiments of a flame retardant cable are provided.The flame retardant cable includes at least one communication elementand a polymeric jacket that surrounds the at least one communicationelement. The polymeric jacket is formed from a flame retardant compoundthat includes a polymer base resin and a flame retardant additivedistributed within the polymer base resin. The flame retardant additiveincludes inclusion complexes that are formed of at least one guestmolecule and at least one carbonific host molecule. Each of the at leastone guest molecules is a polyoxometalate ionic liquid.

Additional features and advantages will be set forth in the detaileddescription that follows, and in part will be readily apparent to thoseskilled in the art from the description or recognized by practicing theembodiments as described in the written description and claims hereof,as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary, and areintended to provide an overview or framework to understand the natureand character of the claims.

The accompanying drawings are included to provide a furtherunderstanding and are incorporated in and constitute a part of thisspecification. The drawings illustrate one or more embodiment(s), andtogether with the description serve to explain principles and theoperation of the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a schematic representation of a flame retardant inclusioncomplex according to an exemplary embodiment;

FIGS. 2A-2B depict an α-cyclodextrin host molecule according to anexemplary embodiment;

FIGS. 3A-3B depict a β-cyclodextrin host molecule according to anexemplary embodiment;

FIGS. 4A-4B depict a γ-cyclodextrin host molecule according to anexemplary embodiment;

FIGS. 5A-5C depict a β-cyclodextrin and ionic liquid modifiedoctamolybdate partial and full inclusion complexes, according to anexemplary embodiment;

FIG. 6 depicts a graphical representation of the limiting oxygen indexof three samples, including a sample containing an inclusion complex,according to an exemplary embodiment; and

FIG. 7 depicts a cable including a flame retardant material according toan exemplary embodiment.

DETAILED DESCRIPTION

Referring generally to the figures, various embodiments of a low-smoke,zero halogen (LSZH) flame retardant compound and its applications areshown. In general, the embodiments discussed herein relate to athermoplastic compound comprised of a polymer, such as a polyolefinhomopolymer or copolymer base resin, and an LSZH flame retardantadditive. The LSZH flame retardant additive includes a carbon source.More specifically, the carbon source is, at least in part, in the formof inclusion complexes in which each inclusion complex has one or morehost molecules and a guest molecule. The host molecule is a carbonificmolecule, and the guest molecule is an ionic liquid (IL) modifiedpolyoxometalate (POM), or as used herein, a polyoxometalate ionic liquid(PIL). The inclusion complex is part of an LSZH flame retardant additivethat can be added to various thermoplastic resins to provide athermoplastic LSZH flame retardant compound. The host and guestmolecules interact physically at the molecular level, such that eachhost molecule is part of a complex with a guest molecule. Thus, duringthe compounding process of a thermoplastic LSZH fire retardant compound,the host molecules are advantageously able to resist aggregating withthe other host molecules, and the guest molecules are advantageouslyable to resist aggregating with the other guest molecules. Bymaintaining an even distribution of inclusion complexes within thecompounded resin, the host and guest molecules are able to react rapidlyand uniformly with the rest of the LSZH flame retardant additivethroughout the thermoplastic compound, providing enhanced flameretardant performance.

FIG. 1 schematically depicts an inclusion complex 10 in which the hostmolecule 12 is one or more carbonific molecules and in which the guestmolecule 14 is one or more PIL. The formation of an inclusion complex 10assures that each carbonific host molecule 12 is provided with a PILguest molecule 14 in close physical proximity, thereby enhancing thespeed and efficiency of the charring process.

The molecules of the inclusion complex 10 are held together by forcesother than covalent bonding, which means that the inclusion complex 10is a physical association, not a chemical reaction. The host molecule 12has an open structure such that the guest molecule 14 can be insertedinto the host molecule 12. In embodiments, the host molecule 12 and theguest molecule 14 are held together through hydrogen bonding, ionicattraction, van der Waals forces, hydrophobic interactions, etc.

In one embodiment, cyclodextrins act as the host molecule 12.Cyclodextrins are cyclic oligosaccharides. In various embodiments, thecyclodextrins used herein are α-, β- and γ-cyclodextrin consisting ofsix, seven, and eight glucopyranose units, respectively. The propertiesof these cyclodextrins are provided in Table 1.

TABLE 1 Properties of Selected Cyclodextrins α β γ Molecule weight(g/mol) 972 1135 1297 Glucose Monomers 6 7 8 Internal cavity diameter(Å) ~5.7 ~6.3 ~7.9 Water solubility (g/100 mL, 25° C.) 14.2 18.5 23.2Melting Point (° C.) ~255 ~265 ~245 Cavity volume (mL/mol) 174 262 462

Structurally, a cyclodextrin molecule consists of (α-1,4)-linkedα-D-glucopyranose units. FIG. 2A provides a line angle formula forα-cyclodextrin; FIG. 3A provides a line-angle formula for3-cyclodextrin; and FIG. 4A provides a line-angle formula forγ-cyclodextrin. Because the glucopyranose units exhibit the chairconformation, each cyclodextrin molecule is shaped like a truncated conehaving a central cavity. The truncated cone shape can be seen in FIGS.2B, 3B, and 4B, which demonstrate that the width of the cone expands asthe cyclodextrin molecule grows with additions of glucopyranose units.The central cavities of cyclodextrin molecules are somewhat lipophilicand hydrophobic, and the outer surface is hydrophilic. The hydroxylfunctional groups are orientated to the cone exterior such that theprimary hydroxyl groups of the each glucopyranose unit (found at thefifth carbon) are located at the narrow edge of the cone and thesecondary hydroxyl groups (located at the second and third carbons ofeach glucopyranose unit) are located at the wider edge. The centralcavity is lined by the skeletal carbons and ethereal oxygens of theglucopyranose units, giving the central cavity of cyclodextrin itslipophilic/hydrophobic character.

The cyclic nature of cyclodextrin allows for other molecules, i.e.,guest molecules, to enter its central cavity. Because of cyclodextrin'shydrophobic central cavity, it will readily form complexes with otherhydrophobic guest molecules. Additionally, because cyclodextrin forms avariety of ring sizes, inclusion complexes between cyclodextrin and avariety differently sized molecules can be created.

While α-, β-, or γ-cyclodextrins are utilized in certain embodiment, avariety of other host molecules can also be utilized, such ascyclodextrins larger than γ-cyclodextrins, chemically modifiedderivatives of the cyclodextrin (such as hydroxypropyl-modifiedcyclodextrin and methyl-modified cyclodextrin), calixarene (having anynumber of repeat units), chemically modified derivatives of calixarene,zeolites, chibaite, urea, thiourea, hydroquinone, and4-p-hydroxyphenyl-2,2,4-trimethylchroman (Dianin's compound). Hostmolecules consisting of urea, thiourea, and hydroquinone formhydrogen-bonded networks that are capable of accommodating guestmolecules. Selection of the host molecule can be done to alter thepolarity of the inclusion complex such that the inclusion complex can betailored to disperse in a variety of different media types.

As discussed above, the guest molecule is a polyoxometalate (POM) thathas been modified with an ionic liquid (IL). Regarding the POM, the POMmakes the charring/carbonization process of the flame retardant additivefaster and more efficient by catalyzing the charring process. Inparticular, the POM helps to create a denser char residue, therebyenhancing flame retardance. Exemplary POM for use in the PIL have thestructure of three or more transition metal oxyanions linked together byshared oxygen atoms to form a large, closed three-dimensional framework.In embodiments, the metal atoms are generally selected from, but are notlimited to, group 5 or group 6 transition metals, such as vanadium(V),niobium(V), tantalum(V), molybdenum(VI), and tungsten(VI). In certainembodiments, the POM is selected for its smoke suppressant properties.In specific smoke suppressant embodiments, the smoke suppressantcontains molybdenum or zinc.

Specific POM anions suitable for use as the PIL include [PW₁₂O₄₀]³⁻,[PMo₁₂O₄₀]³⁻, [SiW₁₂O₄₀]⁴⁻, [SiMo₁₂O₄₀]⁴⁻, [BW₁₂O₄₀]³⁻, [BMo₁₂O₄₀]³⁻,[AsW₁₂O₄₀]⁵⁻, [AsMo₁₂O₄₀]⁵⁻, [GeW₁₂O₄₀]⁴⁻, [GeMo₁₂O₄₀]⁴⁻, [PMo₉V₃O₄₀]⁵⁻,[PMo₁₀V₂O₄₀]⁵⁻, [PMo₁₁VO₄₀]⁴⁻, [P₂W₁₈O₆₂]⁶⁻, [P₂Mo₁₈O₆₂]⁶⁻,[As₂W₁₈O₆₂]⁶⁻, [As₂Mo₁₈O₆₂]⁶⁻, [W₆O₁₉]²⁻, [Mo₆O₁₉]²⁻, [V₆O₁₉]⁸⁻,[Nb₆O₁₉]⁸⁻, among others. Further, in other embodiments, a variety ofmolybdenum-containing POM may be used as the guest molecule, including,but not limited to, molybdenum trioxide, ammonium octamolybdate,molybdenum acetate [Mo₂(acetate)₄], molybdenum dialkyldithiocarbamate,calcium and zinc molybdates, and other organo-molybdenum and/ormolybdenum-containing compounds.

Regarding the IL, in embodiments, the IL includes a cation based on,e.g., ammonium, imidazolium, guanidinium, pyridium, morpholinium,pyridazinium, 1,2,4-triazolium, triazine, sulfonium, phosphazenium, orphosphonium and an anion based on, e.g., sulfates, sulfonates,phosphates, borates, etc. Exemplary IL suitable for forming the PILinclude 1-ethyl-3-methyl-imidazolium ethyl sulfate,1-butyl-3-methylimidazolium hexafluorophosphate,1-butyl-3-methylimidazolium tetrafluoroborate,1-hexyl-3-methylimidazolium hexafluorophosphate,1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide,1-ethyl-3-methylimidazolium trifluoromethanesulfonate, scandium(III)trifluoromethanesulfonate, praseodymium (III) trifluoromethanesulfonate,1,3-dialkyl-1,2,3-triazolium hexafluorophosphate,1,3-dialkyl-1,2,3-triazolium bis(trifluoromethanesulfonyl)imide, and1,2,4-trimethylpyrazolium methyl sulfate, among others. Generally, saltscontaining imidazolium cation, quaternary cationic scales, cationicpyrrole, and/or pyrazole cation are suitable ionic liquids for use inthe PIL. A variety of other ionic liquids suitable for use in thepresent invention are disclosed in U.S. Publication No. 2011/0073331(application Ser. No. 12/947,377, filed on Nov. 16, 2010), the entirecontents of which are incorporated herein by reference thereto.

Before forming the inclusion complex, the POM and IL are reacted toproduce the PIL. In embodiments, the PIL are formed through acid/basereactions or through ion-exchange reactions. For example, in anion-exchange reaction, the IL and salts of the POM are placed in asolvent, such as water, and the cation of the IL will attach to the POManion to form the PIL. The PIL is then removed from the solvent.

Upon obtaining the PIL, the inclusion complex comprised of the PIL guestmolecule and the carbonific host molecule can be formed. In this regard,insertion of the guest molecule into the host molecule does not involvea chemical reaction, i.e., no covalent bonds are broken or formed.Instead, the reaction is purely a physical association based onmolecular attraction. In embodiments, the inclusion complexes are formedby dissolving stoichiometric amounts of the host molecule and the guestmolecule in a solvent. For example, with reference to FIG. 5A, the hostmolecule and guest molecule have been added to the solvent at a ratioCD:PIL of 1:1. However, as shown in FIGS. 5B and 5C, the host moleculeand guest molecule can also be added to the solvent at ratios CD:PIL of,e.g., 2:1 and 3:1, respectively. Indeed, the ratio of CD:PIL for theparticular host molecule (β-cyclodextrin) and guest molecule(1-butyl-3-methylimidazolium phosphomolybdate) can react at ratios ofgreater than 0 and up to 3 (i.e., CD:PIL of >0:1 to 3:1).

By forming inclusion complexes, the individual host and guest moleculesare substantially prevented from aggregating during compounding of athermoplastic compound because one or more of the host molecules arealready matched with a guest molecule. Additionally, the complexes helpto overcome additive insolubility. For instance, a hydrophobic guestmolecule can be inserted into a host molecule that has a hydrophobiccavity and a hydrophilic exterior, such as cyclodextrin. The hydrophilicexterior will allow the complex to dissolve in a hydrophilic solvent,thereby facilitating the dissolution of an otherwise insolvent,hydrophobic guest molecule into a hydrophilic solvent. Further, theclose proximity encourages more rapid reaction kinetics within thecompounded thermoplastic material when exposed to heat and/or fire.

In another aspect, the LSZH flame retardant or intumescent system can becompounded with a base polymer to create a thermoplastic LSZH flameretardant compound. The thermoplastic LSZH flame retardant compound canbe deployed through a variety of means, including paints, sprays, dipcoatings, jacketing materials, wrappers, etc.

In various embodiments, the thermoplastic compound is based on athermoplastic polymer. More specifically, the thermoplastic compound isbased on a polyolefin homopolymer or copolymer resin. Suitablepolyolefin resins include single polymers or a blend of polymersselected from the following types: ethylene-vinyl acetate copolymers,ethylene-acrylate copolymers, polyethylene homopolymers (includes butnot limited to low density, medium density, and high density), linearlow density polyethylene, very low density polyethylene, polyolefinelastomer copolymer, polypropylene homopolymer,polyethylene-polypropylene copolymer, butene- and octene branchedcopolymers, or maleic anhydride-grafted versions of the polymers listedabove. Selection of the polymer depends primarily on the application towhich the thermoplastic flame retardant compound is going to besubjected. In another embodiment, the base resin could be a halogenatedthermoplastic (such as polyvinyl chloride); polyamide 6, 6/6, 11, or 12resins; thermoplastic polyurethane; or a crosslinked polyethylene.

In embodiments, the LSZH flame retardant additive contains other flameretardant components, such as metal hydrates, gas-forming species orcombinations of species (e.g., melamine and its derivatives, etc.), charstrength boosters, etc. In an exemplary embodiment, the flame retardantadditive includes an additional carbonific source, an acid donor, and/ora spumific agent. Exemplary carbonific sources include polyols (e.g.,pentaerythritol, xylitol, mannitol, and d-sorbitol), starch, and/orpolyamide-6. Exemplary acid donors include ammonium polyphosphate,diammonium diphosphate, and/or diammonium pentaborate. An exemplaryspumific agent is melamine; although, ammonium-containing compounds canalso be used as spumific agents in embodiments.

Further, in embodiments, the inclusion complexes can be dispersed in asynergist carrier. A synergist carrier is an inorganic compound, such asa zeolite, a clay, a bentonite, and/or zinc borate, among others, thatoperates with the inclusion complexes to enhance flame retardance and/orsmoke suppression of the flame retardant additive. The synergist carriercan do so in a variety of ways, including, for example, forming aceramic layer in or on the char layer/foam, releasing water whendecomposed to dilute the combustible gases and/or to suppress smoke,thermally insulating the polymer compound, functioning as ananti-dripping agent, and/or, together with the inclusion complexes,promoting the function (e.g., the catalytic effect) on the charringprocess of the flame retardant additive.

Various proportions of each component can be used in formulating thethermoplastic flame retardant compound. In a particular embodiment, theinclusion complex is from 0.1 wt % to 15 wt % of the thermoplastic flameretardant compound. In a more particular embodiment, the inclusioncomplex is from 0.5 wt % to 5 wt % of the thermoplastic flame retardantcompound. In another particular embodiment, the entire flame retardantadditive (e.g., including other carbonifics, acid donors, spumificagents, synergists, etc.) is from 5 wt % to 60 wt % of the thermoplasticflame retardant compound. In a more particular embodiment, the flameretardant additive is from 20 wt % to 40 wt % of the thermoplastic flameretardant compound. Additionally, while the weight percentage of theinclusion complex in the thermoplastic flame retardant compound willdepend, at least to some extent, on the weights of the specific host andguest molecules, the amount of the PIL guest molecules is from 0.1 wt %to 10 wt % in some embodiments.

Further, in embodiments, the thermoplastic compound may also includenon-flame retardant additives such as mineral fillers (talc, calciumcarbonate, etc.), antioxidants, UV additives, processing modifiers,compatibilizers, and other standard polymer additives.

The base resin, LSZH flame retardant additive, and all other additivesare compounded together using elevated temperatures, such as from about140° C. to 220° C. or higher, and sufficient shear, such as at shearrates from 10 s⁻¹ to 10,000 s⁻¹, to distribute the components. In aparticular embodiment, the shear rate for mixing is between 50 s⁻¹ and500 s⁻¹. Sufficient shear mixing can be achieved through use of suchmixing equipment as a co-rotating twin screw extruder, a single screwextruder with mixing zones, a Banbury-style rotary mixer, Buss kneader,or another high-shear mixer. Advantageously, the molecular levelinteraction between the host and guest molecules allows for high shearmixers to be used at a level where the risk of degradation to thepolymer is substantially diminished while still providing excellentdispersion of the flame retardant additive.

Example

FIGS. 5A-5C provide exemplary depictions of an inclusion complex havingβ-cyclodextrin as the host molecules and 1-butyl-3-methylimidazoliumphosphomolybdate as the PIL guest molecule. The PIL was formed through a1:1 molar ratio ion-exchange reaction of 1-butyl-3-methylimidazoliumchloride and ammonium phosphomolybdate in water. During the reaction,the 1-butyl-3-methylimidazolium cation attaches to the phosphomolybdateanion, and the other reaction product of NH₄Cl can be washed away.

The inclusion complex is then formed by dissolving 11.4 g β-cyclodextrinin a 100 mL of solvent comprised of 85 mL water and 15 mL acetone. Theacetone was added to increase the solubility of the β-cyclodextrin. ThePIL of 1-butyl-3-methylimidazolium phosphomolybdate was then added toform the inclusion complexes.

A batch (PP-IC) was compounded including 1 wt % of the β-CD/PILinclusion complex, 19 wt % of a flame retardant mixture of ammoniumpolyphosphate (APP) and pentaerythritol (PER) with APP:PER of 2:1, andthe balance of polypropylene polymer (Pro-fax PH835, available fromLyondellBasell). Additional batches for the purpose of comparison werealso compounded. One comparison batch (PP) was made of purepolypropylene, and another comparison batch (PP control) was made ofpolypropylene mixed with 20 wt % APP/PER with APP:PER of 2:1. Allbatches were compounded using a twin screw extruder (34 mm Twin ScrewExtruder, available from Leistritz Extrusionstechnik GmbH) according tothe processing conditions shown in Table 2. Additionally, all sampleswere then injection molded (using an Allrounder 370C injection moldingmachine, available from Arburg GmbH & Co. KG) into test samples with aprocessing condition as shown in Table 3.

TABLE 2 Compounding Conditions for Flame Retardant Compound Screw Speed(RPM) 100 Single Feeder (kg/hr) 2.25 Twin Screw Feeder (g/min) 9.4 Zone1 (° C.) n/a Zone 2 (° C.) 150 Zone 3 (° C.) 180 Zone 4 (° C.) 180 Zone5 (° C.) 160 Zone 6 (° C.) 160 Zone 7 (° C.) 160 Zone 8 (° C.) 160 Zone9 (° C.) 160 Zone 10 (° C.) 160 Die Temp (° C.) 150 Torque (amps) 9.1Vacuum (in/hg) 5

TABLE 3 Injection molding conditions Gate Temp (° C.) 170 Mold TempMoving Half (° F.) 100 Mold Temp Fixed Half (° F.) 100 Temp Zone 1 (°C.) 170 Temp Zone 2 (° C.) 180 Temp Zone 3 (° C.) 190 Temp Zone 4 (° C.)200 Temp Zone 5 (° C.) 200 Dosage Volume (ccm) 20.5 Holding Pressure BarBase 1 (Bar) 900 Holding Time (s) 3 Step 1: Injection Flow (ccm/s) 60Actual Bar Pressure (Bar) 900 Switch Over Point 1.65 Actual Switch OverPressure (Bar) 1097-1180 Cooling (s) 10

A visual combustion test was first performed on the PP control and thePP-IC samples. The test involved burning the samples with a propanetorch under a hood. The PP control sample exhibited more extensiveburning along its length whereas the PP-IC developed a more extensivechar layer and less burning along its length. The samples were thentested to determine their limiting oxygen index (LOI) in accordance withstandard ISO 4589, including general requirements as specified in ISO4589-1:2017 and further described in ISO 4589-2:2017 and ISO4589-3:2017, the contents of ISO 4589 being incorporated herein byreference. As shown in FIG. 6 and as recorded in Table 4, below, thePP-IC sample had an LOI of 27.5%, whereas the PP and PP control sampleshad an LOI 18.0% and 23.2%, respectively.

TABLE 4 Composition and Flame Retardant Performance of Test Samples PPAPP/PER CD-PIL LOI Samples (wt %) (wt %) (wt %) (%) UL-94 Dripping PP100 0 0 18.0 NR Yes PP control 80 20 0 23.2 NR Yes PP-IC 80 19 1 27.5 V0No

Finally, the samples were tested to determine their UL-94 flammabilityrating, which evaluates burning/afterglow times as well as drippingduring the test. The test involves applying a flame to the end of avertically hanging sample ten times for a period of ten seconds eachtime. After each ten second flame application, the time over which thesample burns after the flame is removed is recorded. Additionally, thesample is observed to determine whether any material drips from thesample and/or ignites the dripping collection material. The highestrating is V-0, which indicates that the sample burned for ten seconds orless after each flame application, the sample burned less than fiftyseconds total after all ten flame applications, the sample exhibitedburning and afterglow of less than thirty seconds after two flameapplications, the sample did not drip, and the sample was not completelyburned. As shown in Table 4, above, the PP-IC sample achieved a UL-94rating of V-0, non-dripping, while the PP sample and the PP controlsample were not able to achieve a UL-94 rating and exhibited dripping.

Advantageously, embodiments of the disclosed inclusion complexes allowfor more efficient and effective use of the flame retardant compounds.For instance, the higher utilization of the flame retardant componentsas a result of decreased aggregation decreases the amount of flameretardant material that is necessary to achieve a given flame retardantperformance. Accordingly, raw material costs are reduced. Alternatively,the same amount of fire retardant material could be used whileincreasing the flame retardant performance, which would improve the burnperformance rating.

The flame retardant thermoplastic compound as described herein can beused for a variety of applications. In embodiments, the thermoplasticLSZH flame retardant compound is used as jacketing for cables, such aselectrical communication cables, optical communication cables, etc. In aparticular embodiment as shown in FIG. 7, the thermoplastic LSZH flameretardant compound is shown as part of an optical fiber cable 20. Cable20 includes a cable body, shown as cable jacket 22, having an innersurface 24 that defines a channel, shown as central bore 26. Pluralitiesof communication elements, shown as optical fibers 28, are locatedwithin bore 26. The cable 20 includes a plurality of core elementslocated within central bore 26. A first type of core element is anoptical transmission core element, and these core elements includebundles of optical fibers 28 that are located within tubes, shown asbuffer tubes 30. Buffer tubes 30 are arranged around a central support,shown as central strength member 34. Central strength member 34 includesan outer coating layer 36. A barrier material, such as water barrier 38,is located around the wrapped buffer tubes 30. An easy access structure,shown as rip cord 39, may be located inside cable jacket 22 tofacilitate access to buffer tubes 30.

In one embodiment, the thermoplastic LSZH flame retardant compound isincorporated into the cable jacket 22 of fiber optic cable 20. Inanother embodiment, the thermoplastic LSZH flame retardant compound isincorporated into the buffer tubes 30 surrounding the bundles of opticalfibers 28. In a further embodiment, the thermoplastic LSZH flameretardant compound is incorporated into the water barrier 38. Bysurrounding the cable and cable components with the thermoplastic LSZHflame retardant compound, the ability of fire to spread along cable 20is reduced, and the amount of smoke produced by cable 20 during fireexposure is reduced.

The inventors envision that cables incorporating the thermoplastic LSZHflame retardant compound discussed above will pass certain flameretardant standards, such as cone calorimeter reaction-to-fire test ISO5660; single cable test IEC 60332-1-2; vertical multi cable test DIN50399/IEC 60332-3-24; and in smoke density chamber IEC 61034.

Unless otherwise expressly stated, it is in no way intended that anymethod set forth herein be construed as requiring that its steps beperformed in a specific order. Accordingly, where a method claim doesnot actually recite an order to be followed by its steps or it is nototherwise specifically stated in the claims or descriptions that thesteps are to be limited to a specific order, it is in no way intendedthat any particular order be inferred. In addition, as used herein, thearticle “a” is intended to include one or more than one component orelement, and is not intended to be construed as meaning only one.

It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thespirit or scope of the disclosed embodiments. Since modifications,combinations, sub-combinations and variations of the disclosedembodiments incorporating the spirit and substance of the embodimentsmay occur to persons skilled in the art, the disclosed embodimentsshould be construed to include everything within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A flame retardant compound comprising: a polymerbase resin; and a flame retardant additive distributed within thepolymer base resin, the flame retardant additive including inclusioncomplexes, wherein each inclusion complex comprises: at least one guestmolecule, wherein each of the at least one guest molecules is apolyoxometalate ionic liquid; and at least one carbonific host molecule;and wherein the flame retardant compound achieves a limiting oxygenindex of at least 25% according to ISO
 4589. 2. The flame retardantcompound of claim 1, wherein the polyoxometalate ionic liquid includespolyoxometalate anions containing molybdenum.
 3. The flame retardantcompound of claim 2, wherein the polyoxometalate anion is derived fromat least one of molybdenum trioxide, ammonium octamolybdate, ammoniumphosphomolybdate, molybdenum acetate, calcium molybdate, zinc molybdate,or molybdenum di alkyldithiocarbamate.
 4. The flame retardant compoundof claim 1, wherein the polyoxometalate ionic liquid is formed from anionic liquid including at least one based on an ammonium, animidazolium, a guanidinium, a pyridium, a morpholinium, a pyridazinium,a 1,2,4-triazolium, a triazine, a sulfonium, a phosphazenium, or aphosphonium and an anion based on a sulfate, a sulfonate, a phosphate,or a borate.
 5. The flame retardant compound of claim 1, wherein the atleast one carbonific host molecule is a cyclodextrin.
 6. The flameretardant compound of claim 5, wherein the cyclodextrin is at least oneof alpha, beta, gamma, or larger cyclodextrins.
 7. The flame retardantcompound of claim 5, wherein the cyclodextrin is a chemically modifiedderivative of cyclodextrin.
 8. The flame retardant compound of claim 1,wherein the at least one carbonific host molecule is at least one ofcalixarene, a chemically modified derivative of calixarene, zeolites,chibaite, urea, thiourea, hydroquinone, or4-p-hydroxyphenyl-2,2,4-trimethylchroman.
 9. The flame retardantcompound of claim 1, wherein the base resin includes at least one ofethylene-vinyl acetate copolymers; ethylene-acrylate copolymers; low,medium, and high density polyethylene homopolymers; linear low densitypolyethylene; very low density polyethylene; polyolefin elastomercopolymer; polypropylene homopolymer; polyethylene-polypropylenecopolymer; butene- and octene branched copolymers; maleicanhydride-grafted versions of the previously listed polyolefins;polyvinyl chloride; polyamide 6; polyamide 6/6; polyamide 11; polyamide12; thermoplastic polyurethane; or crosslinked polyethylene.
 10. Theflame retardant compound of claim 1, wherein the flame retardantadditive further includes at least one of a metal hydrate, a charstrength booster, a synergist, or a gas-forming compound.
 11. The flameretardant compound of claim 1, wherein the flame retardant compound iscomprised of from 0.1 to 15 wt % of the inclusion complexes.
 12. Theflame retardant compound of claim 1, wherein the flame retardantadditive further includes a second carbonific source, an acid donor, anda spumific agent.
 13. The flame retardant compound of claim 12, whereinthe second carbonific source is at least one of a polyol, a starch, orpolyamide-6.
 14. The flame retardant compound of claim 12, wherein theacid donor is at least one of ammonium polyphosphate, diammoniumdiphosphate, or diammonium pentaborate.
 15. The flame retardant compoundof claim 12, wherein a single compound is both the acid donor and thespumific agent.
 16. A flame retardant cable, comprising: at least onecommunication element; a polymeric jacket that surrounds the at leastone communication element, wherein the polymeric jacket is formed from aflame retardant compound comprising: a polymer base resin; a flameretardant additive distributed within the polymer base resin, the flameretardant additive including inclusion complexes, wherein each inclusioncomplex comprises: at least one guest molecule, wherein each of the atleast one guest molecules is a polyoxometalate ionic liquid; and atleast one carbonific host molecule.
 17. The flame retardant cable ofclaim 16, wherein the at least one communication element comprises anoptical fiber.
 18. The flame retardant cable of claim 16, wherein theflame retardant compound achieves a limiting oxygen index of at least25% according to ISO
 4589. 19. The flame retardant cable of claim 16,wherein the flame retardant compound is comprised of 20 wt % or less ofthe flame retardant additive and achieves a V-0 rating according toUL-94.
 20. The flame retardant cable of claim 16, wherein thepolyoxometalate ionic liquid includes polyoxometalate anions containingmolybdenum, wherein the at least one carbonific host molecule is acyclodextrin, and wherein the ratio of carbonific host molecule topolyoxometalate anion is more than 0 and less than or equal to
 3. 21.The flame retardant cable of claim 16, wherein the flame retardantcompound is comprised of from 0.1 to 5 wt % of the inclusion complexes.22. The flame retardant cable of claim 16, wherein the flame retardantadditive further includes a second carbonific source, an acid donor, anda spumific agent.